Chromosomal instability plays a major role in the evolution of malignancy; it may be that the acquisition of genetic instability is an important step in tumorigenicity. We have found that there is a striking correlation between the ability of a cell to form a tumor and the ability of a cell to amplify. Highly tumorigenic cells were found to amplify an endogenous marker gene (CAD) at a rate 60 fold greater than non-tumorigenic cells. In both cases the amplification occurs as a spontaneous event. Normal diploid primary cells lack a detectable frequency of amplification altogether. Given these observations, we would like to know when in the multistep process towards malignancy the ability to amplify genomic sequences is acquirrd and how this change in genomic stability relates to the neoplastic process. This proposal will addrrss these questions through three specific aims. First, we will extend our observations to an independent in vitro model system for cell transformation. We will determine where during the progression from a diploid, stable state to the aneuploid, unstable state the acquisition of the ability to amplify genomic sequences occurs. Second, we will ask whether discrete steps which have been identified in the multistep process of tumorigenesis preceed or follow this acquisition of genetic instability. Specifically, we will ask if the activity which can suppress the transformed phenotype can also suppress the ability of a transformed cell to amplify. Finally, we will examine cells from patients that are highly predisposed to neoplasia and exhibit chromosomal instability for their relative ability to amplify genomic sequences. These experiments will test the hypothesis that increased genomic instability, as measured by gene amplification, may be used as an indicator for increased tumorigenic potential.